I seem to do something like that every now and then (ergo my nickname). If I recall, I reload terminal and xfce4 from gslapt and generally it starts working again. You might have to log in to the tui to get a terminal and use slapt-get. If that didn't work, I would, again from tui, as root go to vasm and select the top option (can't remember its name). That restores some defaults.

Let's see what you have left.Open the run dialog again. Try "xterm" first. If that doesn't work, try it as "/usr/bin/xterm".If one worked, post which one and we'll go from there.If neither worked, try "roxterm" and "/usr/bin/roxterm"; then "lxterminal" and "/usr/bin/lxterminal".If none of that works, start the file manager if you can. Select Tools > Open current folder in terminal (or press F4).Post results.